It might be of interest to US gardeners to know that Imidacloprid (as well as Thiomethoxam) has just been withdrawn from use in the European Union for 2 years while more research is carried out into the effects of neonicotinoids on bee populations. This in response to a report by the European Food Safety Authority which identified potential risks to bee health from the chemicals. Lindens are bee magnets when in bloom. Lindens get very large and attempting to keep them aphid free is going to be an enormous and never ending job. They just get aphids - that is their nature. If that is a real problem to you I would be inclined to choose a different tree. Have you tried just pointing the hose at the tree and spraying it forcefully every so often? Also I don't think there is any point in fertilising an established 24 year old tree. Here is a link that might be useful: Imidacloprid

Perhaps you could put up a second house somewhere near just like the first and give them an alternative. I've had good luck with this when I get birds battling over a box. Of course that's a slippery slope and why I have so many bird houses. Maybe you shouldn't listen to me.

Then that would be ME!! And that's just not happening!! Ive inherited hosting TG & theres way too much stuff to do last minute. Multi-tasking at its finest. I had the dressing in the oven finishing up- added the rolls on the bottom level- took them both out at the same time-- burnt bottom rolls!! Ugh. Re-do on the rolls. Its that time of life where things my mother did have been passed onto me. I'm learning.........but there is Alot to this domestication stuff. Grannies &mamas made it look so easy & relaxed. Goals:)

If you know where the bees most likely have a nest, drill a hole in sheetrock on the inside and spray inside the wall to kill and deter the bees. Fill hole in sheetrock and paint same color as wall.